1. Field of the Invention
The present invention relates to a structure member made of thin metal and an image forming apparatus using such a structure member.
2. Related Background Art
Recently, in copying machines and multi-function printers which are medium-sized office equipment, a sheet supply tray and an automatic both-face device have been incorporated into a body of the equipment and installation space for the equipment and an outer dimension of the equipment have been reduced. In addition, in order to improve operability for users or service men, there has been adopted an arrangement in which less parts are arranged in a front surface of the equipment from which various elements disposed within the equipment can be drawn forwardly so that replenishment of toner and maintenance can be performed at the front surface of the equipment.
In an electrophotographic copying machine shown in FIG. 8, a convey unit portion 7 supporting an image forming portion, regist rollers, a convey portion and a fixing device, sheet supply portions 2, 3, 4 and 5 and a both-face unit portion 6 can be drawn forwardly, and a structure member for supporting such unit portions is shown as a hatched portion 8, and a bottom plate 9 constituting a bottom structure has a small thickness (10 to 30 mm).
In this way, installation space, configuration and arrangement for the structure members such as side plates, bottom plate and stay have been limited more and more. Particularly, although the bottom plate which is the bottom structure is the most important structure member (among all structure members of the apparatus) in view of the fact that it supports the weight of the apparatus, it has been requested that a thickness of the bottom plate is reduced as much as possible to reduce the height of the apparatus and to make the apparatus more compact.
Since the bottom plate is the structure member which must have great rigidity for supporting the weight of the apparatus and holding other front and rear structure members, if the rigidity of the bottom plate is insufficient, various disadvantages will occur. For example, if a floor on which the apparatus is rested is distorted, the bottom plate will be deformed due to the distortion to deform the entire apparatus, so that positional relation between various elements disposed within the apparatus is deviated to result in erroneous operation (particularly, in a copying machine, a precise positional relation between elements contributing to image formation is deviated to result in distortion of an obtained image).
Further, when the apparatus is moved, casters attached to the bottom plate are subjected to great load. In such a case, if the rigidity of the bottom plate to which the casters are attached is insufficient, portions of the bottom plate to which the casters are attached are deformed, thereby causing poor image and/or abnormal operation of the casters.
In order to avoid the above disadvantages, as shown in FIG. 9, drawing areas have been provided on the bottom plate 9 to reinforce the bottom plate or a reinforcement member such as a cross-member has been integrally attached to the bottom plate thereby to increase the rigidity of the bottom plate. However, since these attempts are effected regarding limited areas of the bottom plate, the reinforcing effect is partial and inadequate, the rigidity of the entire bottom plate cannot be improved.
Incidentally, FIG. 9 is a perspective view showing main structure members constituting a medium-sized copying machine and, in FIG. 9, the reference numeral 10 denotes a front side plate; 11 denotes a rear side plate; 12, 13 denote right side stay members; and 14, 15 denote left side stay members. These elements are formed from steel plates having a thickness of about 1 to 3 mm. The front side plate 10 and the rear side plate 11 are joined to the bottom plate 9 and the stay members 12, 13, 14 and 15 are joined to the front side plate 10 and the rear side plate 11 by screws or welding, thereby providing an integral structure member of the copying machine.
Further, since the added reinforcement member cannot improve the rigidity efficiently, effective mating with increase of cost cannot be obtained.
On the other hand, recently, a problem regarding operation noise of the apparatus has been watched and reduction of noise of the apparatus has been requested. However, sources of noise within the apparatus has been increased and, thus, an important technical problem is to prevent the noise from leaking from the apparatus. To solve this problem, it is requested that the rigidity of the structure members of the apparatus is increased to prevent vibration of the structure members caused by the noise sources.
In order to solve this problem, in the past, a member for preventing the vibration (vibration isolating and noise shielding material such as glass wool) has been added. However, such material is very expensive, thereby increasing the cost of the entire apparatus.
However, it is difficult to ensure the adequate rigidity of the structure members as the compactness of the apparatus and improvement in incorporated function (for example, increase of the number of contained sheets) have been requested more and more.